Injection molding of polyarylene sulfide compositions

ABSTRACT

A method for injection molding a thermoplastic composition that contains a polyarylene sulfide and a boron-containing nucleating agent is provided. By selectively controlling certain aspects of the polyarylene sulfide and nucleating agent, as well as the particular manner in which they are combined, the crystallization properties of the resulting thermoplastic composition can be significantly improved. This allows the “cooling time” during a molding cycle to be substantially reduced while still achieving the same degree of crystallization. The cooling time can be represented by the “normalized cooling ratio”, which is determined by dividing the total cooling time by the average thickness of the molded part.

RELATED APPLICATIONS

This application claims filing benefit of U.S. Provisional PatentApplication Ser. No. 61/576,505 filed on Dec. 16, 2011, which isincorporated herein in its entirety.

BACKGROUND OF THE INVENTION

Polyphenylene sulfide (“PPS”) is a high performance polymer that canwithstand high thermal, chemical, and mechanical stresses. Due to itsrelatively slow crystallization rate, however, injection molding ofparts from polyphenylene sulfide can be challenging. For example, toachieve the desired degree of crystallization, molding is generallyconducted at a high mold temperature (˜130° C. or more) and for arelatively long cycle time. Unfortunately, high mold temperaturestypically dictate the need for expensive and corrosive heating mediums(e.g., oil). Attempts to address the problems noted above have generallyinvolved the inclusion of various additives in the polymer compositionto help improve its crystallization properties. To date, however, suchattempts have not been fully satisfactory. In fact, the problems havebecome even more pronounced as various industries (e.g., electronic,automotive, etc.) are now demanding injection molded parts with verysmall dimensional tolerances. In these applications, the polymer musthave good flow properties so that it can quickly and uniformly fill thesmall spaces of the mold cavity. It has been found, however, thatconventional polyphenylene sulfides that manage to meet the requisitehigh flow requirement tend to require a long cooling cycle, which can bea very costly and time consuming step.

As such, a need exists for a suitable method for injection moldingpolyarylene sulfide with a relatively short cycle time while stillachieving good mechanical properties.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method forinjection molding a thermoplastic composition is disclosed. The methodcomprises injecting a thermoplastic composition into a mold cavity,wherein the thermoplastic composition comprises a polyarylene sulfideand a boron-containing nucleating agent; subjecting the thermoplasticcomposition to a cooling cycle to form a molded part having a certainaverage thickness, wherein the cooling cycle has a normalized coolingratio of from about 0.2 to about 8 seconds per millimeter, as determinedby dividing the total time of the cooling cycle by the thickness of themolded part; and ejecting the molded part from the mold cavity.

In accordance with another embodiment of the present invention, a moldedpart is disclosed that is formed from a thermoplastic composition thatcomprises a polyarylene sulfide and boron-containing nucleating agent.For example, in one embodiment a centrifugal pump for circulating acoolant through an automotive engine is disclosed. The pump comprises apump impeller that is configured to flow the coolant radially outwardinto a volute chamber; and a housing that encloses the pump impeller andvolute chamber, wherein at least a portion of the pump impeller, thehousing, or both comprise a molded part formed from the thermoplasticcomposition. In another embodiment, an electronic device is disclosedthat comprises a molded part such as a portion of the housing or acooling fan that is formed from the thermoplastic composition.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE FIGURES

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a cross-sectional view of one embodiment of an injection moldapparatus that may be employed in the present invention; and

FIG. 2 illustrates a water pump that may be formed in accordance withone embodiment of the present invention.

FIG. 3 is a perspective view of an electronic device that can be formedin accordance with one embodiment of the present invention; and

FIG. 4 is a perspective view of the electronic device of FIG. 3, shownin closed configuration.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention.

Generally speaking, the present invention is directed to a method forinjection molding a thermoplastic composition that contains apolyarylene sulfide and a boron-containing nucleating agent. Byselectively controlling certain aspects of the polyarylene sulfide andnucleating agent, as well as the particular manner in which they arecombined, the present inventors have discovered that the crystallizationproperties of the resulting thermoplastic composition can besignificantly improved. Among other things, this allows the “coolingtime” during a molding cycle to be substantially reduced while stillachieving the same degree of crystallization. The cooling time can berepresented by the “normalized cooling ratio”, which is determined bydividing the total cooling time by the average thickness of the moldedpart. As a result of the present invention, for example, the normalizedcooling ratio may range from about 0.2 to about 8 seconds permillimeter, in some embodiments from about 0.5 to about 6 seconds permillimeter, and in some embodiments, from about 1 to about 5 seconds permillimeter. The total cooling time can be determined from the point whenthe composition is injected into the mold cavity to the point that itreaches an ejection temperature at which it can be safely ejected.Exemplary cooling times may range, for instance, from about 1 to about60 seconds, in some embodiments from about 5 to about 40 seconds, and insome embodiments, from about 10 to about 35 seconds. Likewise, exemplaryaverage thicknesses for the molded parts may be about 25 millimeters orless, in some embodiments from about 0.5 to about 15 millimeters, and insome embodiments, from about 1 millimeter to about 10 millimeters.

In addition to minimizing the required cooling time for a molding cycle,the method and composition of the present invention can also allow partsto be molded at lower temperatures while still achieving the same degreeof crystallization. For example, the mold temperature (e.g., temperatureof a surface of the mold) may be from about 50° C. to about 120° C., insome embodiments from about 60° C. to about 110° C., and in someembodiments, from about 70° C. to about 90° C. In addition to minimizingthe energy requirements for the molding operation, such low moldtemperatures may be accomplished using cooling mediums that are lesscorrosive and expensive than some conventional techniques. For example,liquid water may be employed as a cooling medium. Further, the use oflow mold temperatures can also decrease the production of “flash”normally associated with high temperature molding operations. Forexample, the length of any flash (also known as burrs) created during amolding operation may be about 0.17 millimeters or less, in someembodiments about 0.14 millimeters or less, and in some embodiments,about 0.13 millimeters or less.

Various embodiments of the present invention will now be described ingreater detail below.

I. Thermoplastic Composition

A. Polyarylene Sulfide

As noted above, the thermoplastic composition contains at least onepolyarylene sulfide, which is generally able to withstand relativelyhigh temperatures without melting. Although the actual amount may varydepending on desired application, polyarylene sulfide(s) typicallyconstitute from about 30 wt. % to about 95 wt. %, in some embodimentsfrom about 35 wt. % to about 90 wt. %, and in some embodiments, fromabout 40 wt. % to about 80 wt. % of the thermoplastic composition. Thepolyarylene sulfide(s) generally have repeating units of the formula:—[(Ar¹)_(n)—X]_(m)—[(Ar²)_(i)—Y]_(j)—[(Ar³)_(k)—Z]_(l)—[(Ar⁴)_(o)—W]_(p)—wherein,

Ar¹, Ar², Ar³, and Ar⁴ are independently arylene units of 6 to 18 carbonatoms;

W, X, Y, and Z are independently bivalent linking groups selected from—SO₂—, —S—, —SO—, —CO—, —O—, —C(O)O— or alkylene or alkylidene groups of1 to 6 carbon atoms, wherein at least one of the linking groups is —S—;and

n, m, i, j, k, l, o, and p are independently 0, 1, 2, 3, or 4, subjectto the proviso that their sum total is not less than 2.

The arylene units Ar¹, Ar², Ar³, and Ar⁴ may be selectively substitutedor unsubstituted. Advantageous arylene units are phenylene, biphenylene,naphthylene, anthracene and phenanthrene. The polyarylene sulfidetypically includes more than about 30 mol %, more than about 50 mol %,or more than about 70 mol % arylene sulfide (—S—) units. For example,the polyarylene sulfide may include at least 85 mol % sulfide linkagesattached directly to two aromatic rings. In one particular embodiment,the polyarylene sulfide is a polyphenylene sulfide, defined herein ascontaining the phenylene sulfide structure —(C₆H₄—S)_(n)—(wherein n isan integer of 1 or more) as a component thereof.

Synthesis techniques that may be used in making a polyarylene sulfideare generally known in the art. By way of example, a process forproducing a polyarylene sulfide can include reacting a material thatprovides a hydrosulfide ion (e.g., an alkali metal sulfide) with adihaloaromatic compound in an organic amide solvent. The alkali metalsulfide can be, for example, lithium sulfide, sodium sulfide, potassiumsulfide, rubidium sulfide, cesium sulfide or a mixture thereof. When thealkali metal sulfide is a hydrate or an aqueous mixture, the alkalimetal sulfide can be processed according to a dehydrating operation inadvance of the polymerization reaction. An alkali metal sulfide can alsobe generated in situ. In addition, a small amount of an alkali metalhydroxide can be included in the reaction to remove or react impurities(e.g., to change such impurities to harmless materials) such as analkali metal polysulfide or an alkali metal thiosulfate, which may bepresent in a very small amount with the alkali metal sulfide.

The dihaloaromatic compound can be, without limitation, ano-dihalobenzene, m-dihalobenzene, p-dihalobenzene, dihalotoluene,dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl, dihalobenzoicacid, dihalodiphenyl ether, dihalodiphenyl sulfone, dihalodiphenylsulfoxide or dihalodiphenyl ketone. Dihaloaromatic compounds may be usedeither singly or in any combination thereof. Specific exemplarydihaloaromatic compounds can include, without limitation,p-dichlorobenzene; m-dichlorobenzene; o-dichlorobenzene;2,5-dichlorotoluene; 1,4-dibromobenzene; 1,4-dichloronaphthalene;1-methoxy-2,5-dichlorobenzene; 4,4′-dichlorobiphenyl;3,5-dichlorobenzoic acid; 4,4′-dichlorodiphenyl ether;4,4′-dichlorodiphenylsulfone; 4,4′-dichlorodiphenylsulfoxide; and4,4′-dichlorodiphenyl ketone. The halogen atom can be fluorine,chlorine, bromine or iodine, and two halogen atoms in the samedihalo-aromatic compound may be the same or different from each other.In one embodiment, o-dichlorobenzene, m-dichlorobenzene,p-dichlorobenzene or a mixture of two or more compounds thereof is usedas the dihalo-aromatic compound. As is known in the art, it is alsopossible to use a monohalo compound (not necessarily an aromaticcompound) in combination with the dihaloaromatic compound in order toform end groups of the polyarylene sulfide or to regulate thepolymerization reaction and/or the molecular weight of the polyarylenesulfide.

The polyarylene sulfide(s) may be homopolymers or copolymers. Forinstance, selective combination of dihaloaromatic compounds can resultin a polyarylene sulfide copolymer containing not less than twodifferent units. For instance, when p-dichlorobenzene is used incombination with m-dichlorobenzene or 4,4′-dichlorodiphenylsulfone, apolyarylene sulfide copolymer can be formed containing segments havingthe structure of formula:

and segments having the structure of formula:

or segments having the structure of formula:

In another embodiment, a polyarylene sulfide copolymer may be formedthat includes a first segment with a number-average molar mass Mn offrom 1000 to 20,000 g/mol. The first segment may include first unitsthat have been derived from structures of the formula:

where the radicals R¹ and R², independently of one another, are ahydrogen, fluorine, chlorine or bromine atom or a branched or unbranchedalkyl or alkoxy radical having from 1 to 6 carbon atoms; and/or secondunits that are derived from structures of the formula:

The first unit may be p-hydroxybenzoic acid or one of its derivatives,and the second unit may be composed of 2-hydroxynaphthalene-6-carboxylicacid. The second segment may be derived from a polyarylene sulfidestructure of the formula:—[Ar—S]_(q)—

where Ar is an aromatic radical, or more than one condensed aromaticradical, and q is a number from 2 to 100, in particular from 5 to 20.The radical Ar may be a phenylene or naphthylene radical. In oneembodiment, the second segment may be derived frompoly(m-thiophenylene), from poly(o-thiophenylene), or frompoly(p-thiophenylene).

The polyarylene sulfide(s) may be linear, semi-linear, branched orcrosslinked. Linear polyarylene sulfides typically contain 80 mol % ormore of the repeating unit —(Ar—S)—. Such linear polymers may alsoinclude a small amount of a branching unit or a cross-linking unit, butthe amount of branching or cross-linking units is typically less thanabout 1 mol % of the total monomer units of the polyarylene sulfide. Alinear polyarylene sulfide polymer may be a random copolymer or a blockcopolymer containing the above-mentioned repeating unit. Semi-linearpolyarylene sulfides may likewise have a cross-linking structure or abranched structure introduced into the polymer a small amount of one ormore monomers having three or more reactive functional groups. By way ofexample, monomer components used in forming a semi-linear polyarylenesulfide can include an amount of polyhaloaromatic compounds having twoor more halogen substituents per molecule which can be utilized inpreparing branched polymers. Such monomers can be represented by theformula R′X_(n), where each X is selected from chlorine, bromine, andiodine, n is an integer of 3 to 6, and R′ is a polyvalent aromaticradical of valence n which can have up to about 4 methyl substituents,the total number of carbon atoms in R′ being within the range of 6 toabout 16. Examples of some polyhaloaromatic compounds having more thantwo halogens substituted per molecule that can be employed in forming asemi-linear polyarylene sulfide include 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, 1,3-dichloro-5-bromobenzene,1,2,4-triiodobenzene, 1,2,3,5-tetrabromobenzene, hexachlorobenzene,1,3,5-trichloro-2,4,6-trimethylbenzene, 2,2′,4,4′-tetrachlorobiphenyl,2,2′,5,5′-tetra-iodobiphenyl,2,2′,6,6′-tetrabromo-3,3′,5,5′-tetramethylbiphenyl,1,2,3,4-tetrachloronaphthalene, 1,2,4-tribromo-6-methylnaphthalene,etc., and mixtures thereof.

Regardless of the particular structure, the number average molecularweight of the polyarylene sulfide is typically about 15,000 g/mol ormore, and in some embodiments, about 30,000 g/mol or more. In certaincases, a small amount of chlorine may be employed during formation ofthe polyarylene sulfide. Nevertheless, the polyarylene sulfide willstill have a low chlorine content, such as about 1000 ppm or less, insome embodiments about 900 ppm or less, in some embodiments from about 1to about 800 ppm, and in some embodiments, from about 2 to about 700ppm. In certain embodiments, however, the polyarylene sulfide isgenerally free of chlorine or other halogens.

B. Boron-Containing Nucleating Agent

A boron-nucleating agent is also employed in the thermoplasticcomposition of the present invention to enhance the crystallizationproperties of the composition. Such nucleating agents typicallyconstitute from about 0.01 wt. % to about 6 wt. %, in some embodimentsfrom about 0.05 wt. % to about 3 wt. %, and in some embodiments, fromabout 0.1 wt. % to about 2 wt. % of the thermoplastic composition.Suitable boron-containing nucleating agents may include, for instance,boron nitride, sodium tetraborate, potassium tetraborate, calciumtetraborate, etc., as well as mixtures thereof. Boron nitride (BN) hasbeen found to be particularly beneficial. Boron nitride exists in avariety of different crystalline forms (e.g., h-BN—hexagonal, c-BN—cubicor spharlerite, and w-BN—wurtzite), any of which can generally beemployed in the present invention. The hexagonal crystalline form isparticularly suitable due to its stability and softness.

C. Other Additives

In addition to the nucleating agent and polyarylene sulfide, thethermoplastic composition may also contain a variety of other differentcomponents to help improve its overall properties. One suitable additivethat may be employed to improve the mechanical properties of thecomposition is an impact modifier. Examples of suitable impact modifiersmay include, for instance, polyepoxides, polyurethanes, polybutadiene,acrylonitrile-butadiene-styrene, polysiloxanes etc., as well as mixturesthereof. In one particular embodiment, a polyepoxide modifier isemployed that contains at least two oxirane rings per molecule. Thepolyepoxide may be a linear or branched, homopolymer or copolymer (e.g.,random, graft, block, etc.) containing terminal epoxy groups, skeletaloxirane units, and/or pendent epoxy groups. The monomers employed toform such polyepoxides may vary. In one particular embodiment, forexample, the polyepoxide modifier contains at least one epoxy-functional(meth)acrylic monomeric component. The term “(meth)acrylic” includesacrylic and methacrylic monomers, as well as salts or esters thereof,such as acrylate and methacrylate monomers. Suitable epoxy-functional(meth)acrylic monomers may include, but are not limited to, thosecontaining 1,2-epoxy groups, such as glycidyl acrylate and glycidylmethacrylate. Other suitable epoxy-functional monomers include allylglycidyl ether, glycidyl ethacrylate, and glycidyl itoconate.

If desired, additional monomers may also be employed in the polyepoxideto help achieve the desired melt viscosity. Such monomers may vary andinclude, for example, ester monomers, (meth)acrylic monomers, olefinmonomers, amide monomers, etc. In one particular embodiment, forexample, the polyepoxide modifier includes at least one linear orbranched α-olefin monomer, such as those having from 2 to 20 carbonatoms and preferably from 2 to 8 carbon atoms. Specific examples includeethylene, propylene, 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene,1-pentene; 1-pentene with one or more methyl, ethyl or propylsubstituents; 1-hexene with one or more methyl, ethyl or propylsubstituents; 1-heptene with one or more methyl, ethyl or propylsubstituents; 1-octene with one or more methyl, ethyl or propylsubstituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. Particularly desired α-olefin comonomers areethylene and propylene. In one particularly desirable embodiment of thepresent invention, the polyepoxide modifier is a copolymer formed froman epoxy-functional (meth)acrylic monomeric component and α-olefinmonomeric component. For example, the polyepoxide modifier may bepoly(ethylene-co-glycidyl methacrylate). One specific example of asuitable polyepoxide modifier that may be used in the present inventionis commercially available from Arkema under the name Lotader® AX8840.Lotader® AX8950 has a melt flow rate of 5 g/10 min and has a glycidylmethacrylate monomer content of 8 wt. %.

Still another suitable additive that may be employed to improve themechanical properties of the thermoplastic composition is anorganosilane coupling agent. The coupling agent may, for example, be anyalkoxysilane coupling agent as is known in the art, such asvinlyalkoxysilanes, epoxyalkoxysilanes, aminoalkoxysilanes,mercaptoalkoxysilanes, and combinations thereof. Aminoalkoxysilanecompounds typically have the formula: R⁵—Si—(R⁶)₃, wherein R⁵ isselected from the group consisting of an amino group such as NH₂; anaminoalkyl of from about 1 to about 10 carbon atoms, or from about 2 toabout 5 carbon atoms, such as aminomethyl, aminoethyl, aminopropyl,aminobutyl, and so forth; an alkene of from about 2 to about 10 carbonatoms, or from about 2 to about 5 carbon atoms, such as ethylene,propylene, butylene, and so forth; and an alkyne of from about 2 toabout 10 carbon atoms, or from about 2 to about 5 carbon atoms, such asethyne, propyne, butyne and so forth; and wherein R⁶ is an alkoxy groupof from about 1 to about 10 atoms, or from about 2 to about 5 carbonatoms, such as methoxy, ethoxy, propoxy, and so forth. In oneembodiment, R⁵ is selected from the group consisting of aminomethyl,aminoethyl, aminopropyl, ethylene, ethyne, propylene and propyne, and R⁶is selected from the group consisting of methoxy groups, ethoxy groups,and propoxy groups. In another embodiment, R⁵ is selected from the groupconsisting of an alkene of from about 2 to about 10 carbon atoms such asethylene, propylene, butylene, and so forth, and an alkyne of from about2 to about 10 carbon atoms such as ethyne, propyne, butyne and so forth,and R⁶ is an alkoxy group of from about 1 to about 10 atoms, such asmethoxy group, ethoxy group, propoxy group, and so forth. A combinationof various aminosilanes may also be included in the mixture.

Some representative examples of aminosilane coupling agents that may beincluded in the mixture include aminopropyl triethoxysilane, aminoethyltriethoxysilane, aminopropyl trimethoxysilane, aminoethyltrimethoxysilane, ethylene trimethoxysilane, ethylene triethoxysilane,ethyne trimethoxysilane, ethyne triethoxysilane,aminoethylaminopropyltrimethoxysilane, 3-aminopropyl triethoxysilane,3-aminopropyl trimethoxysilane, 3-aminopropyl methyl dimethoxysilane or3-aminopropyl methyl diethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-methyl-3-aminopropyl trimethoxysilane,N-phenyl-3-aminopropyl trimethoxysilane,bis(3-aminopropyl)tetramethoxysilane, bis(3-aminopropyl)tetraethoxydisiloxane, and combinations thereof. The amino silane may also be anaminoalkoxysilane, such as γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, γ-aminopropylmethyldimethoxysilane,γ-aminopropylmethyldiethoxysilane,N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane,N-phenyl-γ-aminopropyltrimethoxysilane,γ-diallylaminopropyltrimethoxysilane andγ-diallylaminopropyltrimethoxysilane. One suitable amino silane is3-aminopropyltriethoxysilane which is available from Degussa, SigmaChemical Company, and Aldrich Chemical Company.

Fillers may also be employed in the thermoplastic composition to helpachieve the desired properties and/or color. When employed, such mineralfillers typically constitute from about 5 wt. % to about 60 wt. %, insome embodiments from about 10 wt. % to about 50 wt. %, and in someembodiments, from about 15 wt. % to about 45 wt. % of the thermoplasticcomposition. Clay minerals may be particularly suitable for use in thepresent invention. Examples of such clay minerals include, for instance,talc (Mg₃Si₄O₁₀(OH)₂), halloysite (Al₂Si₂O₅(OH)₄), kaolinite(Al₂Si₂O₅(OH)₄), illite ((K,H₃O)(Al,Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O)]),montmorillonite (Na,Ca)_(0.33)(Al,Mg)₂Si₄O₁₀(OH)₂.nH₂O), vermiculite((MgFe,Al)₃(Al,Si)₄O₁₀(OH)₂.4H₂O), palygorskite((Mg,Al)₂Si₄O₁₀(OH).4(H₂O)), pyrophyllite (Al₂Si₄O₁₀(OH)₂), etc., aswell as combinations thereof. In lieu of, or in addition to, clayminerals, still other mineral fillers may also be employed. For example,other suitable silicate fillers may also be employed, such as calciumsilicate, aluminum silicate, mica, diatomaceous earth, wollastonite, andso forth. Mica, for instance, may be a particularly suitable mineral foruse in the present invention. There are several chemically distinct micaspecies with considerable variance in geologic occurrence, but all haveessentially the same crystal structure. As used herein, the term “mica”is meant to generically include any of these species, such as muscovite(KAl₂(AlSi₃)O₁₀(OH)₂), biotite (K(Mg,Fe)₃(AlSi₃)O₁₀(OH)₂), phlogopite(KMg₃(AlSi₃)O₁₀(OH)₂), lepidolite (K(Li,Al)₂₋₃(AlSi₃)O₁₀(OH)₂),glauconite (K,Na)(Al,Mg,Fe)₂(Si,Al)₄O₁₀(OH)₂), etc., as well ascombinations thereof.

Fibrous fillers may also be employed in the thermoplastic composition.When employed, such fibrous fillers typically constitute from about 5wt. % to about 60 wt. %, in some embodiments from about 10 wt. % toabout 50 wt. %, and in some embodiments, from about 15 wt. % to about 45wt. % of the thermoplastic composition. The fibrous fillers may includeone or more fiber types including, without limitation, polymer fibers,glass fibers, carbon fibers, metal fibers, and so forth, or acombination of fiber types. In one embodiment, the fibers may be choppedglass fibers or glass fiber rovings (tows). Fiber diameters can varydepending upon the particular fiber used and are available in eitherchopped or continuous form. The fibers, for instance, can have adiameter of less than about 100 μm, such as less than about 50 μm. Forinstance, the fibers can be chopped or continuous fibers and can have afiber diameter of from about 5 μm to about 50 μm, such as from about 5μm to about 15 μm.

Lubricants may also be employed in the thermoplastic composition thatare capable of withstanding the processing conditions of poly(arylenesulfide) (typically from about 290° C. to about 320° C.) withoutsubstantial decomposition. Exemplary of such lubricants include fattyacids esters, the salts thereof, esters, fatty acid amides, organicphosphate esters, and hydrocarbon waxes of the type commonly used aslubricants in the processing of engineering plastic materials, includingmixtures thereof. Suitable fatty acids typically have a backbone carbonchain of from about 12 to about 60 carbon atoms, such as myristic acid,palmitic acid, stearic acid, arachic acid, montanic acid, octadecinicacid, parinric acid, and so forth. Suitable esters include fatty acidesters, fatty alcohol esters, wax esters, glycerol esters, glycol estersand complex esters. Fatty acid amides include fatty primary amides,fatty secondary amides, methylene and ethylene bisamides andalkanolamides such as, for example, palmitic acid amide, stearic acidamide, oleic acid amide, N,N′-ethylenebisstearamide and so forth. Alsosuitable are the metal salts of fatty acids such as calcium stearate,zinc stearate, magnesium stearate, and so forth; hydrocarbon waxes,including paraffin waxes, polyolefin and oxidized polyolefin waxes, andmicrocrystalline waxes. Particularly suitable lubricants are acids,salts, or amides of stearic acid, such as pentaerythritol tetrastearate,calcium stearate, or N,N′-ethylenebisstearamide. When employed, thelubricant(s) typically constitute from about 0.05 wt. % to about 1.5 wt.%, and in some embodiments, from about 0.1 wt. % to about 0.5 wt. % ofthe thermoplastic composition.

Still another additive that may be employed in the thermoplasticcomposition is a disulfide compound. Without wishing to be bound by anyparticular theory, the disulfide compound can undergo a polymer scissionreaction with a polyarylene sulfide during melt processing that evenfurther lowers the overall melt viscosity of the composition. Whenemployed, disulfide compounds typically constitute from about 0.01 wt. %to about 3 wt. %, in some embodiments from about 0.02 wt. % to about 1wt. %, and in some embodiments, from about 0.05 to about 0.5 wt. % ofthe composition. The ratio of the amount of the polyarylene sulfide tothe amount of the disulfide compound may likewise be from about 1000:1to about 10:1, from about 500:1 to about 20:1, or from about 400:1 toabout 30:1. Suitable disulfide compounds are typically those having thefollowing formula:R³—S—S—R⁴

wherein R³ and R⁴ may be the same or different and are hydrocarbongroups that independently include from 1 to about 20 carbons. Forinstance, R³ and R⁴ may be an alkyl, cycloalkyl, aryl, or heterocyclicgroup. In certain embodiments, R³ and R⁴ are generally nonreactivefunctionalities, such as phenyl, naphthyl, ethyl, methyl, propyl, etc.Examples of such compounds include diphenyl disulfide, naphthyldisulfide, dimethyl disulfide, diethyl disulfide, and dipropyldisulfide. R³ and R⁴ may also include reactive functionality at terminalend(s) of the disulfide compound. For example, at least one of R³ and R⁴may include a terminal carboxyl group, hydroxyl group, a substituted ornon-substituted amino group, a nitro group, or the like. Examples ofcompounds may include, without limitation, 2,2′-diaminodiphenyldisulfide, 3,3′-diaminodiphenyl disulfide, 4,4′-diaminodiphenyldisulfide, dibenzyl disulfide, dithiosalicyclic acid, dithioglycolicacid, α,α′-dithiodilactic acid, β,β′-dithiodilactic acid,3,3′-dithiodipyridine, 4,4′dithiomorpholine,2,2′-dithiobis(benzothiazole), 2,2′-dithiobis(benzimidazole),2,2′-dithiobis(benzoxazole) and 2-(4′-morpholinodithio)benzothiazole.

Still other additives that can be included in the composition mayinclude, for instance, antimicrobials, pigments, antioxidants,stabilizers, surfactants, waxes, flow promoters, solid solvents, andother materials added to enhance properties and processability.

The manner in which the boron-containing nucleating agent, polyarylenesulfide, and other optional additives are combined may vary as is knownin the art. For instance, the materials may be supplied eithersimultaneously or in sequence to a melt processing device thatdispersively blends the materials. Batch and/or continuous meltprocessing techniques may be employed. For example, a mixer/kneader,Banbury mixer, Farrel continuous mixer, single-screw extruder,twin-screw extruder, roll mill, etc., may be utilized to blend and meltprocess the materials. One particularly suitable melt processing deviceis a co-rotating, twin-screw extruder (e.g., Leistritz co-rotating fullyintermeshing twin screw extruder). Such extruders may include feedingand venting ports and provide high intensity distributive and dispersivemixing. For example, the polyarylene sulfide and nucleating agent may befed to the same or different feeding ports of a twin-screw extruder andmelt blended to form a substantially homogeneous melted mixture. Meltblending may occur under high shear/pressure and heat to ensuresufficient dispersion. For example, melt processing may occur at atemperature of from about 50° C. to about 500° C., and in someembodiments, from about 100° C. to about 250° C. Likewise, the apparentshear rate during melt processing may range from about 100 seconds⁻¹ toabout 10,000 seconds⁻¹, and in some embodiments, from about 500seconds⁻¹ to about 1,500 seconds⁻¹. Of course, other variables, such asthe residence time during melt processing, which is inverselyproportional to throughput rate, may also be controlled to achieve thedesired degree of homogeneity.

Besides melt blending, other techniques may also be employed to combinethe nucleating agent and the polyarylene sulfide. For example, thenucleating agent may be supplied during one or more stages of thepolymerization of the polyarylene sulfide, such as to the polymerizationapparatus. Although it may be introduced at any time, it is typicallydesired to apply the nucleating agent before polymerization has beeninitiated, and typically in conjunction with the precursor monomers forthe polyarylene sulfide. The reaction mixture is generally heated to anelevated temperature within the polymerization reactor vessel toinitiate melt polymerization of the reactants.

Regardless of the manner in which they are combined together, the degreeand rate of crystallization may be significantly enhanced by thenucleation system of the present invention. For example, thecrystallization potential of the thermoplastic composition (prior tomolding) may be about 52% or more, in some embodiments about 55% ormore, in some embodiments about 58% or more, and in some embodiments,from about 60% to about 95%. The crystallization potential may bedetermined by subtracting the latent heat of crystallization (ΔH_(c))from the latent heat of fusion (ΔH_(f)), dividing this difference by thelatent heat of fusion, and then multiplying by 100. The latent heat offusion (ΔH_(f)) and latent heat of crystallization (ΔH_(c)) may bedetermined by Differential Scanning calorimetry (“DSC”) as is well knownin the art and in accordance with ISO Standard 10350. The latent heat ofcrystallization may, for example, be about 15 Joules per gram (“J/g”) orless, in some embodiments about 12 J/g or less, and in some embodiments,from about 1 to about 10 J/g. The latent heat of fusion may likewise beabout 15 Joules per gram (“J/g”) or more, in some embodiments about 18J/g or more, and in some embodiments, from about 20 to about 28 J/g.

In addition, the thermoplastic composition may also crystallize at alower temperature than would otherwise occur absent the presence of thenucleating agent. For example, the crystallization temperature (prior tomolding) of the thermoplastic composition may about 250° C. or less, insome embodiments from about 100° C. to about 245° C., and in someembodiments, from about 150° C. to about 240° C. The melting temperatureof the thermoplastic composition may also range from about 250° C. toabout 320° C., and in some embodiments, from about 265° C. to about 300°C. The melting and crystallization temperatures may be determined as iswell known in the art using differential scanning calorimetry inaccordance with ISO Test No. 11357. Even at such melting temperatures,the ratio of the deflection temperature under load (“DTUL”), a measureof short term heat resistance, to the melting temperature may stillremain relatively high. For example, the ratio may range from about 0.65to about 1.00, in some embodiments from about 0.70 to about 0.99, and insome embodiments, from about 0.80 to about 0.98. The specific DTULvalues may, for instance, range from about 230° C. to about 300° C., insome embodiments from about 240° C. to about 290° C., and in someembodiments, from about 250° C. to about 280° C. Such high DTUL valuescan, among other things, allow the use of high speed processes oftenemployed during the manufacture of components having a small dimensionaltolerance.

The present inventors have also discovered that the thermoplasticcomposition may possess a relatively low melt viscosity, which allows itto readily flow into the mold cavity during production of the part. Forinstance, the composition may have a melt viscosity of about 20 poise orless, in some embodiments about 15 poise or less, and in someembodiments, from about 0.1 to about 10 poise, as determined by acapillary rheometer at a temperature of 316° C. and shear rate of 1200seconds⁻¹. Among other things, these viscosity properties can allow thecomposition to be readily injection molded into parts having very smalldimensions without producing excessive amounts of flash.

II. Injection Molding

The method of the present invention includes the injection of thethermoplastic composition into a mold cavity where it is cooled untilreaching the desired ejection temperature. As discussed above, theunique properties of the thermoplastic composition of the presentinvention can allow the cooling time and/or mold temperature of amolding cycle to be substantially reduced while still achieving the samedegree of crystallization. In addition to improving the properties ofthe cooling cycle, other aspects of the molding operation may also beenhanced. For example, as is known in the art, injection can occur intwo main phases—i.e., an injection phase and holding phase. During theinjection phase, the mold cavity is completely filled with the moltenthermoplastic composition. The holding phase is initiated aftercompletion of the injection phase in which the holding pressure iscontrolled to pack additional material into the cavity and compensatefor volumetric shrinkage that occurs during cooling. After the shot hasbuilt, it can then be cooled. In addition to reducing the cooling timeas discussed above, the improved properties of the thermoplasticcomposition may also allow for a lower holding time, which includes thetime required to pack additional material into the cavity and the timeat which this material is held at a certain pressure. Once cooling iscomplete, the molding cycle is completed when the mold opens and thepart is ejected, such as with the assistance of ejector pins within themold.

Any suitable injection molding equipment may generally be employed inthe present invention. Referring to FIG. 1, for example, one embodimentof an injection molding apparatus or tool 10 that may be employed in thepresent invention is shown. In this embodiment, the apparatus 10includes a first mold base 12 and a second mold base 14, which togetherdefine an article or component-defining mold cavity 16. The moldingapparatus 10 also includes a resin flow path that extends from an outerexterior surface 20 of the first mold half 12 through a sprue 22 to amold cavity 16. The resin flow path may also include a runner and agate, both of which are not shown for purposes of simplicity. Thethermoplastic composition may be supplied to the resin flow path using avariety of techniques. For example, the thermoplastic composition may besupplied (e.g., in the form of pellets) to a feed hopper attached to anextruder barrel that contains a rotating screw (not shown). As the screwrotates, the pellets are moved forward and undergo pressure andfriction, which generates heat to melt the pellets. Additional heat mayalso be supplied to the composition by a heating medium that iscommunication with the extruder barrel. One or more ejector pins 24 mayalso be employed that are slidably secured within the second mold half14 to define the mold cavity 16 in the closed position of the apparatus10. The ejector pins 24 operate in a well-known fashion to remove amolded part from the cavity 16 in the open position of the moldingapparatus 10.

A cooling mechanism may also be provided to solidify the resin withinthe mold cavity. In FIG. 1, for instance, the mold bases 12 and 14 eachinclude one or more cooling lines 18 through which a cooling mediumflows to impart the desired mold temperature to the surface of the moldbases for solidifying the molten material. As noted above, the presentinventors have found that the improved crystallization properties of thethermoplastic composition can allow it to be molded at lower moldtemperatures than previously thought possible. In addition to minimizingthe energy requirements for the molding operation, such lower moldtemperatures may also be achieved using mechanisms that are lesscorrosive and expensive than some conventional techniques. For example,liquid water may be employed as the cooling medium and may be heated toa temperature within the ranges noted above.

As a result of the injection molding technique employed in the presentinvention, it has been discovered that the thermoplastic composition canbe readily formed into parts having a wide range of different parts. Theparts may be in the form of a substrate having an average thickness ofabout 25 millimeters or less, in some embodiments from about 0.5 toabout 15 millimeters, and in some embodiments, from about 1 millimeterto about 10 millimeters. Alternatively, the part may simply possesscertain features (e.g., walls, ridges, etc.) within the averagethickness ranges noted above.

Regardless of the particular size, the present inventors have discoveredthat excellent mechanical properties can be achieved even whenrelatively short cooling times are employed. For instance, an injectionmolded part may exhibit a tensile strength of from about 100 to about500 MPa, in some embodiments from about 120 to about 400 MPa, and insome embodiments, from about 190 to about 350 MPa. The part may alsoexhibit a tensile break strain of about 0.5% or more, in someembodiments from about 0.6% to about 10%, and in some embodiments, fromabout 0.8% to about 3.5%; and/or a tensile modulus of from about 5,000MPa to about 25,000 MPa, in some embodiments from about 8,000 MPa toabout 22,000 MPa, and in some embodiments, from about 10,000 MPa toabout 20,000 MPa. The tensile properties may be determined in accordancewith ISO Test No. 527 (technically equivalent to ASTM D638) at 23° C.The parts may also exhibit a flexural strength of from about 20 to about500 MPa, in some embodiments from about 50 to about 400 MPa, and in someembodiments, from about 100 to about 350 MPa; a flexural break strain ofabout 0.5% or more, in some embodiments from about 0.6% to about 10%,and in some embodiments, from about 0.8% to about 3.5%; and/or aflexural modulus of from about 5,000 MPa to about 25,000 MPa, in someembodiments from about 8,000 MPa to about 22,000 MPa, and in someembodiments, from about 10,000 MPa to about 20,000 MPa. The flexuralproperties may be determined in accordance with ISO Test No. 178(technically equivalent to ASTM D790) at 23° C. The part may alsopossess a high impact strength, such as an Izod notched impact strengthgreater than about 4 kJ/m², in some embodiments from about 5 to about 40kJ/m², and in some embodiments, from about 6 to about 30 kJ/m², measuredat 23° C. according to ISO Test No. 180) (technically equivalent to ASTMD256, Method A).

With such excellent mechanical properties, the resulting injectionmolded parts may be employed in a wide variety of different components.One particular component that may incorporate an injection molded partof the present invention is a liquid pump (e.g., water pump). The liquidpump may be a direct lift pump, positive displacement pump (e.g.,rotary, reciprocating, or linear), rotodynamic pump (e.g., centrifugal),gravity pump, etc. Rotodynamic pumps, in which energy is continuouslyimparted to the pumped fluid by a rotating impeller, propeller, orrotor, are particularly suitable. In a centrifugal pump, for instance,fluid enters a pump impeller along or near to the rotating axis and isaccelerated by the impeller, flowing radially outward into a diffuser orvolute chamber, from which it exits into the downstream piping. Suchpumps are often used in automotive applications to move a coolantthrough the engine. Due to the high temperatures associated withautomotive engines, the injection molded composition of the presentinvention is particularly well suited for use in the centrifugal pumpsof such automotive cooling systems. In certain embodiments, for example,all or a portion (e.g., blades) of the water impeller may be formed fromthe injection molded composition of the present invention. Centrifugalpumps also generally include a housing that encloses certain componentsof the pump and protects them from heat, corrosion, etc. In someembodiments, some or all of the housing may be formed from the injectionmolded composition of the present invention.

Referring to FIG. 2, one particular example of a centrifugal pump isshown that can employ the injection molded composition of the presentinvention. In the illustrated embodiment, the pump contains a rotaryshaft 201 supported on a housing 203 via a bearing 202. A pump impeller204, which may contain the injection molded composition of the presentinvention, is rigidly fixed at an end of the rotary shaft 201. A pulleyhub 205 is also rigidly fixed on the base end portion of the rotaryshaft 201. Between the bearing 202 and the pump impeller 204, amechanical seal 206 is formed that is constituted by a stationary member206 a fixed on the side of the housing 203 and a rotary member 206 bfixedly engaged with the rotary shaft 201. The pump may also include ahousing 207, which can contain the injection molded composition of thepresent invention. The housing 207 may be affixed to the pump housing203 (e.g., with fastening bolts) so that a volute chamber 208 is definedtherebetween. While not illustrated, a suction portion and a dischargeport may also be provided within the housing 207.

Of course, the injection molded composition is not limited to theformation of water pumps or portions thereof, and it may be utilized informing all manner of components as may be incorporated in a fluidhandling system including pipes and sections of pipes, flanges, valves,valve seats, seals, sensor housings, thermostats, thermostat housings,diverters, linings, propellers, and so forth. The composition may alsoemployed in forming components that function in a fluid environment,such as consumer products that encounter high temperature fluids, e.g.,heated beverage containers. Still further, the composition may beemployed in completely different environments, such as an electroniccomponent. Examples of electronic components that may employ such amolded part include, for instance, cellular telephones, laptopcomputers, small portable computers (e.g., ultraportable computers,netbook computers, and tablet computers), wrist-watch devices, pendantdevices, headphone and earpiece devices, media players with wirelesscommunications capabilities, handheld computers (also sometimes calledpersonal digital assistants), remote controllers, global positioningsystem (GPS) devices, handheld gaming devices, battery covers, speakers,camera modules, integrated circuits (e.g., SIM cards), etc.

Wireless electronic devices, however, are particularly suitable.Examples of suitable wireless electronic devices may include a desktopcomputer or other computer equipment, a portable electronic device, suchas a laptop computer or small portable computer of the type that issometimes referred to as “ultraportables.” In one suitable arrangement,the portable electronic device may be a handheld electronic device.Examples of portable and handheld electronic devices may includecellular telephones, media players with wireless communicationscapabilities, handheld computers (also sometimes called personal digitalassistants), remote controls, global positioning system (“GPS”) devices,and handheld gaming devices. The device may also be a hybrid device thatcombines the functionality of multiple conventional devices. Examples ofhybrid devices include a cellular telephone that includes media playerfunctionality, a gaming device that includes a wireless communicationscapability, a cellular telephone that includes game and email functions,and a handheld device that receives email, supports mobile telephonecalls, has music player functionality and supports web browsing.

Referring to FIGS. 3-4, one particular embodiment of an electronicdevice 100 is shown as a portable computer. The electronic device 100includes a display member 103, such as a liquid crystal diode (LCD)display, an organic light emitting diode (OLED) display, a plasmadisplay, or any other suitable display. In the illustrated embodiment,the device is in the form of a laptop computer and so the display member103 is rotatably coupled to a base member 106. It should be understood,however, that the base member 106 is optional and can be removed inother embodiments, such as when device is in the form of a tabletportable computer. Regardless, in the embodiment shown in FIGS. 3-4, thedisplay member 103 and the base member 106 each contain a housing 86 and88, respectively, for protecting and/or supporting one or morecomponents of the electronic device 100. The housing 86 may, forexample, support a display screen 120 and the base member 106 mayinclude cavities and interfaces for various user interface components(e.g., keyboard, mouse, and connections to other peripheral devices).Although the thermoplastic composition of the present invention maygenerally be employed to form any portion of the electronic device 100,for example for forming the cooling fan, it is typically employed toform all or a portion of the housing 86 and/or 88. When the device is atablet portable computer, for example, the housing 88 may be absent andthe thermoplastic composition may be used to form all or a portion ofthe housing 86. Regardless, due to the unique properties achieved by thepresent invention, the housing(s) or a feature of the housing(s) may bemolded to have a very small wall thickness, such as within the rangesnoted above.

Although not expressly shown, the device 100 may also contain circuitryas is known in the art, such as storage, processing circuitry, andinput-output components. Wireless transceiver circuitry in circuitry maybe used to transmit and receive radio-frequency (RF) signals.Communications paths such as coaxial communications paths and microstripcommunications paths may be used to convey radio-frequency signalsbetween transceiver circuitry and antenna structures. A communicationspath may be used to convey signals between the antenna structure andcircuitry. The communications path may be, for example, a coaxial cablethat is connected between an RF transceiver (sometimes called a radio)and a multiband antenna.

The present invention may be better understood with reference to thefollowing examples.

Test Methods

Melt Viscosity:

The melt viscosity is determined as scanning shear rate viscosity anddetermined in accordance with ISO Test No. 11443 (technically equivalentto ASTM D3835) at a shear rate of 1200 s⁻¹ and at a temperature of 316°C. using a Dynisco 7001 capillary rheometer. The rheometer orifice (die)had a diameter of 1 mm, a length of 20 mm, an L/D ratio of 20.1, and anentrance angle of 180°. The diameter of the barrel was 9.55 mm±0.005 mmand the length of the rod was 233.4 mm.

Thermal Properties:

The thermal properties are determined by differential scanningcalorimetry (“DSC”) in accordance with ISO Test No. 11357. Under the DSCprocedure, samples are heated and cooled at 20° C. per minute as statedin ISO Standard 10350 using DSC measurements conducted on a TA Q100Instrument. For both pellet and mold samples, the heating and coolingprogram is a 2-cycle test that begins with an equilibration of thechamber to 25° C., followed by a first heating period at a heating rateof 20° C. per minute to a temperature of 320° C., followed byequilibration of the sample at 320° C. for 1 minutes, followed by afirst cooling period at a cooling rate of 20° C. per minute to atemperature of 50° C., followed by equilibration of the sample at 50° C.for 1 minute, and then a second heating period at a heating rate of 20°C. per minute to a temperature of 320° C. The results are evaluatedusing a TA software program, which identifies and quantifies the meltingtemperature, the endothermic and exothermic peaks, and the areas underthe peaks on the DSC plots. The areas under the peaks on the DSC plotsare determined in terms of joules per gram of sample (J/g). For example,the heat of fusion of a resin or mold sample is determined byintegrating the area of the endothermic peak. The area values aredetermined by converting the areas under the DSC plots (e.g., the areaof the endotherm) into the units of joules per gram (J/g) using computersoftware. The exothermic heat of crystallization is determined duringthe first cooling cycle and the second heating cycle. The percentcrystallization potential may also be calculated as follows:% crystallization potential=100*(A−B)/A

wherein,

A is the sum of endothermic peak areas (e.g., 1st heat of fusion); and

B is the sum of exothermic peak areas (e.g., pre-crystallization heat offusion).

Tensile Modulus, Tensile Stress, and Tensile Elongation:

Tensile properties are tested according to ISO Test No. 527 (technicallyequivalent to ASTM D638). Modulus and strength measurements are made onthe same test strip sample having a length of 80 mm, thickness of 10 mm,and width of 4 mm. The testing temperature is 23° C., and the testingspeeds are 1 or 5 mm/min.

Flexural Modulus, Flexural Stress, and Flexural Strain:

Flexural properties are tested according to ISO Test No. 178(technically equivalent to ASTM D790). This test is performed on a 64 mmsupport span. Tests are run on the center portions of uncut ISO 3167multi-purpose bars. The testing temperature is 23° C. and the testingspeed is 2 mm/min.

Izod Notched Impact Strength:

Notched Izod properties are tested according to ISO Test No. 180(technically equivalent to ASTM 0256, Method A). This test is run usinga Type A notch. Specimens are cut from the center of a multi-purpose barusing a single tooth milling machine. The testing temperature is 23° C.

Deflection Under Load Temperature (“DTUL”):

The deflection under load temperature is determined in accordance withISO Test No. 75-2 (technically equivalent to ASTM D648-07). A test stripsample having a length of 80 mm, thickness of 10 mm, and width of 4 mmis subjected to an edgewise three-point bending test in which thespecified load (maximum outer fibers stress) is 1.8 MPa. The specimen islowered into a silicone oil bath where the temperature is raised at 2°C. per minute until it deflects 0.25 mm (0.32 mm for ISO Test No. 75-2).

Flash:

To determine flash, the sample is initially dried at 135° C. for 3 to 4hours. The sample is then injection molded into a dual tab flash moldusing the following conditions: melt temperature of 321° C., injectiontime of 1.5 seconds, injection pressure of 30,000 psi, hold time andpressure of 10 seconds at 1,000 psi, and screw retraction time of 20seconds. More particularly, the sample is injected so that 0.5 inches ofone tab is filled in 1.5 seconds with resin and 0.75 inches of the othertab remains unfilled. After cooling, the flash of the parts is measuredwith a Proscan instrument coupled with Image Pro Plus software.

Example 1

The components listed in Table 1 below are mixed in a Werner PfleidererZSK 25 co-rotating intermeshing twin-screw extruder with an 18 mmdiameter.

TABLE 1 Sample Components Glass FORTRON ® Boron Fibers 0205 NitrideGlycolube P Aminosilane (4 mm) Sample PPS (wt. %) (wt. %) (wt. %) (wt.%) (wt. %) 1 59.3 — 0.3 0.4 40.0 2 59.1 0.2 0.3 0.4 40.0

The thermal properties of pellets formed from the samples aredetermined, the results of which are set forth below in Table 2.

TABLE 2 Thermal Properties Pre- Pre- 1^(st) 2^(nd) Re- Cryst Cryst Heat,1^(st) Heat, 2^(nd) Re- Cryst Melt Heat of Melt Heat of Melt Heat ofCryst Heat of Cryst MV Temp Fusion Temp Fusion Temp Fusion Temp FusionPotential Sample (poise) (° C.) (J/g) (° C.) (J/g) (° C.) (J/g) (° C.)(J/g) (%) 1 2648 126.1 11.1 280.9 22.7 277.4 22.2 214.3 23.1 51.1 2 2590124.8 8.2 281.0 21.3 280.8 21.4 236.5 23.6 61.4

As indicated above, the addition of the boron nitride nucleating agentincreased the crystallization potential of the composition.

Pellets formed from the Samples 1-2 are also molded into T-bars(thickness of 3 millimeters) on a Mannesmann Demag D100 NCIII injectionmolding machine at various different cooling cycle times and/or moldtemperatures. The mechanical properties are tested, the results of whichare set forth below in Table 3.

TABLE 3 Mechanical Properties Cooling Normalized Tensile Mold CycleCooling stress Temp. Time Ratio (5 mm/min) DTUL Flash Sample (° C.) (s)(s/mm) (MPa) (° C.) (mm) 1 135 25.0 8.3 195 272 0.50 90 25.0 8.3 188 2700.14 90 12.5 4.2 187 270 — 60 25.0 8.3 193 268 0.07 65 12.5 4.2 188 268— 2 135 25.0 8.3 194 273 0.65 90 25.0 8.3 194 273 0.19 90 12.5 4.2 194273 — 60 25.0 8.3 191 272 0.10 65 12.5 4.2 197 272 —

As indicated above, Sample 2 (containing boron nitride) generallyexhibited better mechanical properties when the cooling cycle timeand/or mold temperature is reduced. For example, at a cooling time of12.5 seconds (Normalized Cooling Ratio of 4.2 s/mm) and mold temperatureof 65° C., Sample 2 achieved a tensile stress of 197 MPa, while Sample 1was only able to achieve a tensile stress of 188 MPa.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A method for injection molding a thermoplasticcomposition, the method comprising: injecting a thermoplasticcomposition into a mold cavity, wherein the thermoplastic compositioncomprises a polyarylene sulfide, an organosilane coupling agent, andboron nitride, and wherein the composition has a crystallizationpotential of about 52% or more, as determined by differential scanningcalorimetry; subjecting the thermoplastic composition to a cooling cycleto form a molded part having a certain average thickness, wherein thecooling cycle has a normalized cooling ratio of from about 0.2 to about8 seconds per millimeter, as determined by dividing the total time ofthe cooling cycle by the thickness of the molded part; and ejecting themolded part from the mold cavity.
 2. The method of claim 1, wherein thenormalized cooling ratio is from about 1 to about 5 seconds permillimeter.
 3. The method of claim 1, wherein the total time of thecooling cycle is from about 5 to about 40 seconds, and wherein theaverage thickness of the molded part is from about 0.5 to about 15millimeters.
 4. The method of claim 1, wherein the mold temperature isfrom about 50° C. to about 120° C.
 5. The method of claim 1, wherein themold temperature is from about 70° C. to about 90° C.
 6. The method ofclaim 1, wherein the water is used as a cooling medium during thecooling cycle.
 7. The method of claim 1, wherein polyarylene sulfidesconstitute from about 30 wt. % to about 95 wt. % of the composition andboron nitride boron-containing nucleating agents constitutes from about0.01 wt % to about 6 wt. % of the composition.
 8. The method of claim 1,wherein the boron nitride includes hexagonal boron nitride.
 9. Themethod of claim 1, wherein the composition further comprises an impactmodifier, mineral filler, fibrous filler, lubricant, disulfide, or acombination thereof.
 10. The method of claim 1, wherein the molded parthas a tensile strength of from about 100 to about 500 MPa, as determinedin accordance with ISO Test No. 527 at 23° C.
 11. The method of claim 1,wherein the molded part has a tensile strength of from about 120 toabout 400 MPa, as determined in accordance with ISO Test No. 527 at 23°C.
 12. An injection molded part formed according to the method ofclaim
 1. 13. A liquid pump comprising the injection molded part of claim12.
 14. The liquid pump of claim 13, wherein the pump is a direct liftpump, positive displacement pump, rotodynamic pump, or gravity pump. 15.The liquid pump of claim 13, wherein the pump is a centrifugal pump forcirculating a coolant through an automotive engine.
 16. An electroniccomponent comprising the injection molded part of claim
 12. 17. Theelectronic component of claim 16, wherein the component is a cellulartelephone, laptop computer, small portable computer, wrist-watch device,pendant device, headphone or earpiece device, media player with wirelesscommunication capabilities, handheld computer, remote controller, globalpositioning system device, handheld gaming device, battery cover,speaker, camera module, or integrated circuit.
 18. The method of claim1, wherein the thermoplastic composition further comprises glass fibers.